Non-equilibrium sound propagation using the orientation-free discrete kinetic theory

Computations using orientation-free discrete velocity models for the dispersion relationship of ultrasound propagation in monatomic hard-sphere gases (or gases composed of systems of vortices) are presented. Comparisons with previous verified fixed-orientation results for the propagation of the sound mode of ultrasound in rarefied gases show that if collective excitations are considered, orientation-free discrete velocity models can provide more physical insight. We also address the symmetry and limits of these models.